Crater formation by nanoparticle impact: contributions of gas, melt and plastic flow

Abstract

The processes underlying crater formation by energetic nanoparticle impact are investigated using molecular dynamics simulations. Both metallic and van-der-Waals-bonded targets are studied. We find a transition from crater formation by melt flow at small impact energies to an evaporation (gas flow) mechanism at higher energies. The transition occurs gradually at impact energies per atom of a few tens of the cohesive energy of the target. van-der-Waals-bonded solids do not exhibit the melt flow cratering regime, in agreement with the narrow liquid zone in their phase diagram. We find that the size of the target region heated above the critical temperature roughly corresponds to the crater volume. The transition shows up most clearly in the increase of the volume of ejected material relative to the crater volume. Finally, we demonstrate the punching of dislocations below the crater for high-velocity impact into ductile targets, leading to a contribution of plastic flow to the crater volume.